1. Field of the Invention
The present invention relates to a vibrating gyroscope, and more particularly to a vibrating gyroscope used for an anti-shaking device for a camera, a car navigation system, a pointing device, or the like.
2. Description of the Related Art
In FIGS. 4 and 5 are shown an example of a conventional vibrating gyroscope. A vibrating gyroscope 1 includes a rectangular-parallelepiped vibrating unit 2. The vibrating unit 2 has two adjacent plate-shaped piezoelectric bodies 3 and 4. The piezoelectric bodies 3 and 4 are polarized in opposite directions. The vibrating unit 2 further has an intermediate electrode 5 formed between the piezoelectric bodies 3 and 4. On the piezoelectric body 3 is formed an electrode 6, and on the piezoelectric body 4 is formed an electrode 7. The electrode 6 on the piezoelectric body 3 is separated into six electrode portions 6a to 6f by grooves. The intermediate electrode 5 is provided with supporting members 8 around nodes of the bending vibration of the vibrating unit 2. The supporting members 8 are used to support the vibrating unit 2, and are connected to a reference potential.
The sum of output signals from the electrode portions 6c and 6d, in the center of the longitudinal direction of the piezoelectric body 3, is input to an amplification circuit 9 as a feedback signal. The output signal from the amplification circuit 9 is adjusted by a gain control amplifier 10 so that the amplitude of the output signal is constant and input to a phase correction circuit 11. The phase of the output signal is corrected by a phase correction circuit 11 and the output signal from the phase correction circuit 11 is supplied to the electrode 7 as a driving signal. Thus, the amplification circuit 9, the gain control amplifier 10 and the phase correction circuit 11 constitute a driving circuit 16 which receives the feedback signal and output the driving signal.
On the other hand, the difference between the output signals from the electrode portions 6c and 6d is output from a differential circuit 12. The output signal of the differential circuit 12 is detected in synchronization with a signal from the phase correction circuit 11 in a synchronous detection circuit 13. The output signal from the synchronous detection circuit 13 is smoothed by a smoothing circuit 14, and is further amplified by a DC amplification circuit 15.
In the vibrating gyroscope 1, the intermediate electrode 5 is connected to the reference potential and the driving signal from the phase correction circuit 11 is applied to the electrode 7. This causes the piezoelectric body 4 to vibrate. Since the piezoelectric body 4 is bonded to the piezoelectric body 3, the whole vibrating unit 2 vibrates under the bending mode in a direction perpendicular to the surfaces with the electrodes 6 and 7. This bending vibration of the vibrating unit 2 also bends the piezoelectric body 3, and the signals corresponding to the bending are output from the electrode portions 6c and 6d. The sum of the output signals is input to the amplification circuit 9.
During the above-explained operation, an electric signal as the driving signal is first converted to a mechanical vibration at the piezoelectric body 4. The mechanical vibration at the piezoelectric body 4 is then transmitted to the piezoelectric body 3 and causes the mechanical vibration at the piezoelectric body 3. Finally, the mechanical vibration at the piezoelectric body 3 is converted to another electric signal as the output signal used for the feedback signal. Due to these conversions, there arises a phase difference between the driving signal input to the vibrating unit 2 and the output signal from the vibrating unit 2. This means that the oscillation frequency under the bending mode of the vibrating unit 2 is shifted with respect to the resonance frequency under the bending mode of the vibrating unit 2.
In order for the vibrating unit 2 to be self-excited and for the vibrating unit 2 and the driving circuit 16 to constitute an oscillation circuit which oscillates constantly, it is necessary that the driving signal which will be generated based on the output signal from the vibrating unit 2 and input to the vibrating unit 2 next time has the original phase which was previously input to the vibrating unit 2. Otherwise, the driving signal input to the vibrating unit 2 each time would have a different phase, and the oscillation circuit having the vibrating unit 2 and the driving circuit 16 cannot reach a constant state so that the vibrating unit 2 can be self-excited.
Normally, vibration gain becomes maximum with a phase differences of 90 degrees and the vibrating unit 2 is so designed that the output signal from the vibrating unit 2 and the driving signal input to the vibrating unit 2 has the phase difference of 90 degrees. Accordingly, the phase correction circuit 11 is used to correct the phase difference of 90 degrees between the driving signal and the feedback signal.
While not rotating, the vibrating unit 2 vibrates under the bending mode perpendicularly to the surfaces with the electrodes 6 and 7 formed thereon, which causes the output signals from the electrode portions 6c and 6d to be similar, and a signal is not output from the differential circuit 12. When the vibrating unit 2 rotates on its axis, a Coriolis force changes the vibrating direction of the vibrating unit 2. This generates a difference between the detection signals from the electrode portions 6c and 6d, and the signal difference is output from the differential circuit 12. The output signal of the differential circuit 12 is detected by the synchronous circuit 13 and is smoothed by the smoothing circuit 14 before it is amplified by the dc amplification circuit 15, whereby a DC signal corresponding to rotational angular velocity can be obtained.
In the aforementioned conventional vibrating gyroscope, the intermediate electrode 5 of the vibrating unit 2 needs to be connected to the reference potential This causes a complicated interconnection for the intermediate electrode 5. In addition, capacitors, resistors and so forth, must be used to form the phase correction circuit 11. Therefore, there arises a problem that the sensitivity and temperature characteristics of the vibrating gyroscope 1 change depending on the deviation of the capacitance, resistance or the like of the capacitors and resistors used in the vibrating gyroscope 1.
Moreover, the deviation of the capacitance, resistance or the like of the capacitors and resistors causes the change or fluctuation of the phase of the detection signals, which further causes the detection timing by the synchronous detection circuit 13 to shift easily. This results in drift of the output signal from the DC amplification circuit 15 and deterioration of the temperature characteristics.
In the case where the vibrating unit is operated at a low frequency of 500 kHz or less, a capacitor used in the phase correction circuit 11 must have a large capacitance, which makes it impossible to include the phase correction circuit 11 in an integrated circuit. Consequently, the number of circuit components used increases, thereby causing a cost increase and preventing the vibrating gyroscope from being made small.
Accordingly, there arises a demand for a vibrating gyroscope which can solve the aforementioned drawbacks associated with the conventional vibrating gyroscope.